1. Field of the invention
This invention relates to an optical card which serves as an optical memory, a card holder for holding the optical card, and an apparatus for recording, reproducing, and erasing information on and from the optical card.
2. Description of the prior art
In recent years, optical memories have come to public notice as high density and high capacity memories. As such optical memories, read-only type compact disks and video disks, add-on type optical disks, and rewritable type optical disks are known. The read-only type compact disks and video disks have already built up a wide market, and various research and development efforts have been made with respect to the add-on type and rewritable type optical disks,in order to enlarge the application of optical memories. In addition to these disk-shaped optical memories, card-shaped optical memories, which are called optical cards, have also attracted much attention as high capacity and portable memories.
FIG. 12 shows a conventional optical card, which comprises a substrate 71 and an optical storage medium 72. The substrate 71 of the optical card 70 is constituted by a thin plate in the shape of a rectangular parallelepiped, and is made of a plastic material such as polycarbonate. The optical storage medium 72 is in the form of a sheet, so as to be disposed on and incorporated with the substrate 71. A plurality of guide tracks 72a are formed on the optical storage medium 72 so as to be parallel with one end face 73 in the direction of length of the substrate 71, resulting in the formation of tracks 72b between the guide tracks 72a. When the tracks 72b are irradiated with light beams moving along the guide tracks 72a, the recording, reproducing, or erasing operation of information is conducted. During these operations, the optical card 70 is usually driven together with the card holder in the direction parallel to the end face 73 of the substrate 71, as described below.
FIG. 13 shows a conventional card holder, which is used for holding the optical card 70 during the operations of recording, reproducing, or erasing information on and from the optical card. The card holder comprises a table 81 with a shallow concave portion 82 to be loaded with the optical card 70. One edge portion in the direction of width of the concave portion 82 is provided with a pin 83 and the other edge portion is provided with a movable lever 85 for pushing the optical card 70 against the pin 83 by force of a coiled spring 84. One inner side 86 defining the concave portion 82 functions as a guide face for guiding the optical card 70, and the other inner side face is provided with a flat spring 87 for pressing the optical card 70 against the inner side 86. When the conventional card holder is loaded with the optical card 70, the optical card 70 is guided along the inner face 86 of the concave portion 82 in the direction indicated by the arrow of FIG. 13, so that its end face 73 faces the inner side 86 of the concave portion 82. The optical card 70 is allowed to slide on the bottom face of the concave portion 82 while being pressed by the flat spring 87 against the inner side 86 of the concave portion 82, until the end face in the direction of width of the optical card 70 comes to the stopper 83. The optical card 70 is then pressed by the movable lever 85 against the stopper 83, so that it can be in a fixed position on the table 81 of the card holder with its end face 73 abutting on the inner side 86 of the concave portion 82. Thereafter, the card holder is disposed on a belt 88 as described below and driven in the direction parallel to the inner side 86, so that the recording, reproducing, or erasing operation of information on and from the optical card 70 is carried out.
However, with the conventional card holder of this type, the optical card 70 in the concave portion 82 is unavoidably subjected to the pressing forces which are parallel to the surface of the optical card 70, so that the optical card 70, which has the substrate 71 constituted by a plastic thin plate, is easily warped by the pressing forces, resulting in the lifting of the optical storage medium 72 off the surface of the table 81. When the tracks 72b of the optical storage medium 72 which are lifted off the surface of the table 81 are scanned with light beams, the tracks 72b are not kept within the depth of focus of light beams, so that the operation of recording, reproducing, or erasing information on and from the optical card 70 is conducted incompletely. Moreover, since light beams are usually converged on the surface of the tracks 72b after passing through the substrate 71, the depth at which light beams are focused varies due to the curved substrate 71 of the optical card 70, so that light beams with a fixed diameter cannot be obtained.
It also happens that an optical card 70 in which the end face 73 and the guide tracks 72a of the optical storage medium 72 are not exactly parallel with each other is unintentionally produced. When such an optical card 70 is moved together with the conventional card holder, the guide tracks 72a deviate from the desired routes, so that autotracking of light beams along the guide tracks 72a becomes inaccurate. Even when an optical card in which the end face 73 and the guide tracks 72a of the optical storage medium 72 are exactly parallel to each other is used, the end face 73 of the optical card 70, which is made of a plastic material, is eventually worn out in the course of frequent use because the end face 73 is repeatedly pressed against the inner face 86 of the conventional card holder whenever the operation of recording, reproducing, or erasing information on and from the optical card is conducted, resulting in an optical card 70 in which the end face 73 and the guide tracks 72a are not exactly parallel to each other any longer. Accordingly, autotracking of light beams, which is satisfactorily conducted at first, becomes inaccurate as the end face 73 becomes worn out in the course of frequent use, so that the operation of recording, reproducing, or erasing information on and from the optical card 70 is conducted only with inaccuracy.